The primary nerve fibers to the penis are from the dorsal nerve of the penis, a branch of the pudendal nerve. The cavernosal nerves are a part of the autonomic nervous system and incorporate both sympathetic and parasympathetic fibers. They travel posterolaterally along the prostate and enter the corpora cavernosa and corpus spongiosum to regulate blood flow during erection and detumescence. The dorsal somatic nerves are also branches of the pudendal nerves. They are primarily responsible for penile sensation. 
The inflatable type of device consists of cylinders that are implanted in the corpora cavernosa, a fluid reservoir implanted in the abdomen, and a pump placed in the scrotum. The man squeezes the pump to move fluid into the cylinders and cause them to become rigid. (He reverses the process by squeezing the pump again.) While these devices allow for intermittent erections, they have a slightly higher malfunction rate than the silicon rods.
The key to this line is to act chill. An occasional soft dick ain’t no thang. But if you get angry, throw off the sheets, and stomp around the apartment while your partner sits in bed watching a grown man throw a temper tantrum, it becomes a thang. Throw out an apology to cover your bases, and then let it go. Once again for the guys in the back: Women understand about not always being able to get wet. And we really understand about not being able to get off every time. One in three women has trouble reaching orgasm during sex. I get that it’s not the exact same thing, but we’re empathetic. A good rule of thumb for almost all insecurities is the less of a big deal you make about something, the less others will.
The risk of impotence increases with age. It is four-fold higher in men in their 60s compared with those in their 40s according to a study published in the Journal of Urology (2000;163:460-463). Men with less education are also more likely to experience impotence, perhaps because they tend to have less healthy lifestyles, eat a less healthy diet, drink more and exercise less. Physical exercise tends to lessen the risk of impotence.
For many men, stopping smoking is an erectile dysfunction remedy, particularly when ED is the result of vascular disease, which occurs when blood supply to the penis becomes restricted because of blockage or narrowing of the arteries. Smoking and even smokeless tobacco can also cause the narrowing of important blood vessels and have the same negative impact.
To examine what is known about the demographics, etiology, risk factors, pathophysiology, diagnostic assessment, treatments (both generic and cause-specific), and the understanding of their consequences by the public and the medical community, the National Institute of Diabetes and Digestive and Kidney Diseases and the Office of Medical Applications of Research of the National Institutes of Health, in conjunction with the National Institute of Neurological Disorders and Stroke and the National Institute on Aging, convened a consensus development conference on male impotence on December 7-9, 1992. After 1 1/2 days of presentations by experts in the relevant fields involved with male sexual dysfunction and erectile impotence or dysfunction, a consensus panel comprised of representatives from urology, geriatrics, medicine, endocrinology, psychiatry, psychology, nursing, epidemiology, biostatistics, basic sciences, and the public considered the evidence and developed answers to the questions that follow.
Another study compared the response of surgically and medically castrated rabbits to vardenafil with that of control rabbits.  Castrated rabbits did not respond to vardenafil, whereas noncastrated rabbits did respond appropriately. This result suggests that a minimum amount of testosterone is necessary for PDE5 inhibitors to produce an erection.
In some cases, ED can be a warning sign of more serious disease. One study suggests ED is a strong predictor of heart attack, stroke, and death from cardiovascular disease. The researchers say all men diagnosed with ED should be evaluated for cardiovascular disease. This does not mean every man with ED will develop heart disease, or that every man with heart disease has ED, but patients should be aware of the link.